This invention pertains to a voltage converting method and apparatus, and more particularly to a method and apparatus for converting voltage with a DC to DC switching converter.
Many devices and circuits need multiple voltage or current levels to operate. Further, many devices utilize batteries for power, such as portable devices. However, batteries only supply a single voltage level. Therefore, devices and circuits requiring multiple voltage levels often employ DC-to-DC converters to provide the various voltage levels needed.
DC-to-DC switching converters are capable of maintaining a constant output voltage by monitoring the output voltage and adjusting the amount of time energy is supplied to an output. In this manner, an output capacitor remains fully charged under a variety of load conditions. The output can generate a larger output voltage or a smaller output voltage across the capacitor by adjusting the amount of time the DC-to-DC converter stores or delivers energy.
Many devices have DC-to-DC switching converters or switchers that utilize DC-to-DC converters to provide voltage conversion, for example, from a high voltage to a lower voltage. Examples of these devices include, cellular telephones, personal digital assistants (PDA), notebook computers, and many other devices. Often these devices have a plurality of power demands. For example, often these devices have a standby mode or low quiescent state and an active mode, where very little power is needed during standby mode and a significantly larger amount of power is needed in the active mode.
The DC-to-DC converter provides the conversion from a high voltage (for example, 30V) to a lower voltage (for example, 2.5V). When providing conversion, the DC-to-DC converter requires a certain amount of power to operate and provide the conversion. One of the drawbacks with utilizing a DC-to-DC converter is at low power demand the efficiency of the DC-to-DC converter is significantly reduced. As the load current decreases on a DC-to-DC converter its efficiency will decrease as the fixed losses associated with its operation become a larger percentage compared to the output power.
FIG. 1 shows a typical efficiency curve 110 of the operation of a DC-to-DC converter. The vertical axis represents the efficiency of the converter, defined as a percentage of the amount of power needed to operate the DC-to-DC converter versus the power supplied by the DC-to-DC converter. The horizontal axis represents a logarithmic scale of the amount of output current supplied by the DC-to-DC converter. As the amount of output current drops the efficiency begins to drop. As the output current continues to drop the efficiency of the DC-to-DC converter is significantly reduced to well below 80%. Because of the fixed operational power loss associated with the operation of the DC-to-DC converter, the operation power loss becomes a larger percentage of total power as the demand on output power is reduced through a reduction in output current. Hence, the efficiency of the converter decreases when operating to provide lower output currents. Thus operating devices which utilize DC-to-DC converters have a reduced efficiency at times where the output demand is lower, such as in standby mode. This can significantly reduce the operating life of batteries utilized to power devices.
The present invention provides an apparatus and method for optimizing the efficiency of a switching converter for converting a first voltage to a second voltage. In one embodiment, the apparatus includes a regulator, a converter and a controller. The controller couples with both the regulator and converter, and the controller is configured to activate and deactivate the regulator and the converter depending on an output demand. In one embodiment, the controller is configured to activate the regulator and deactivate the converter when the output demand falls from a first demand level to a second demand level. The controller is further configured to activate the converter and to deactivate the regulator when the output demand rises from the second demand level to the first demand level. The apparatus is configured to monitor the demand, and to activate the converter when the demand is at a first level or activate the regulator when the demand is at a second level. The apparatus is further configured to deactivate the regulator when the demand is at the first level and to deactivate the converter when the demand is at the second level. In one embodiment, the demand is at the second level when operating in a standby mode. In one embodiment, the demand is at the first level when the demand exceeds a threshold.
In one embodiment, the apparatus and method is incorporated into electronic devices which operate at a plurality of voltage levels. These devices include devices operating with energy storage cells, such as batteries. In one embodiment, the apparatus and method of the present invention utilize the bimodal mode of the electronic device to signal the controller to transition between supplying the load from the converter or the regulator.
In one embodiment, the apparatus is implemented on a single integrated circuit, or integrated as part of a larger single integrated circuit.